1. Field of the Invention
The present invention generally relates to an image-forming apparatus supervising system which includes a plurality of data communication apparatuses each connecting with one or more image-forming apparatuses, such as copiers and printers, and a central control apparatus (herein after referred to as a center system) connecting with the plurality of data communication apparatuses via a communication line.
2. Discussion of the Background
An image-forming apparatus supervising system, a system capable of connecting a plurality of image-forming apparatuses (i.e., copiers or the like which include a remote diagnosis) disposed at an office or the like with unspecified users (i.e., customers) to a center system disposed at sales or service bases (i.e., company) or the like, using a data communication apparatus and a communication line such as for example a public line, is generally known.
In such an image-forming apparatus supervising system, the center system subsequently executes an obtaining (i.e., a collecting) operation for obtaining usage information, such as a total copy count value of an applicable image-forming apparatus, which is transmitted from each communication apparatus when a self-generating call is made by the data communication apparatus or when the center system gets access thereto on a predetermined closing day (e.g., 5th day of every month). The center system then automatically submits a bill corresponding to the usage information obtained.
In such a conventional image-forming apparatus supervising system, it is unsure whether the center system correctly obtains usage information of all image-forming apparatuses (i.e, all the image-forming apparatuses connected via the communication line and each data communication apparatus) by circumstances occurring in the image-forming apparatus, the data communication apparatus, and the communication line such as for example as indicated in the following items (1) through (5):                (1) A problem occurs in the line;        (2) A line is disconnected because of moving of a customer;        (3) Communication is interrupted during transmission of usage information by the data communication apparatus because a facsimile (FAX) or a telephone connected to the data communication apparatus is utilized;        (4) The data communication apparatus could not transmit usage information because of a busy state (BUSY) of the center system side; or        (5) The center system could not get access to the data communication apparatus because the FAX or telephone connected to the data communication apparatus is utilized.        
Then, in the above noted conventional image-forming apparatus supervising system when the center system could not correctly obtain the usage information of all the applicable image-forming apparatuses, the above-noted obtaining operation is executed again several times. Thus, there exists at times a case in which usage information of all applicable image-forming apparatuses is not correctly obtained.